The topic of analog circuit simulation has been extensively studied ever since the advent of integrated circuits over three decades ago. Recently, the remarkable evolution of the wireless/personal electronics market has introduced numerous new analog/RF products, as well as new challenges for the simulation of such systems. In order to conquer the increasing difficulties encountered in IC simulation, many advanced techniques; including steady-state analysis and envelope following have been developed. At the same time, the advance of very large scale integration (VLSI) technologies has made it possible to integrate an entire mixed-signal system onto a single chip or within a single electronic package. It is, therefore, important to evaluate the performance of the full mixed-signal system during both top-down design and bottom-up verification.
As IC technologies scale to finer feature sizes and circuit applications move to higher frequency bands, the behavior of analog/RF circuits becomes more complicated and more difficult to understand. Although only a small section of the entire mixed-signal system operates with truly analog signals, the design and verification of the analog components is generally the most challenging. Furthermore, design specifications are not only defined for individual analog/RF circuit blocks, but detailed high-level specifications are described for the entire analog/RF subsystem. For example, an analog front-end in the wireless transceiver is evaluated by several system-level specifications such as ACPR (adjacent channel power ratio). Such specifications require that the analog/RF subsystem is verified independently, as an intermediate stage between circuit-level analysis and mixed-signal system-level simulation.
An example of a simulator that applies circuit-level analysis to a circuit is shown in FIG. 1. Simulator 100 accepts a circuit description that is obtained at process box 102, and produces the output response at process box 104. Such a simulator works by first building equations that describe the overall circuit at process box 106. Often, such a simulator uses modified nodal analysis (MNA) to produce the equations. These equations, which can be both linear and nonlinear, are solved at process box 108.
Unfortunately, directly applying or extending existing simulation techniques to analog/RF system-level analysis suffers from serious limitations. For example, a complete analog/RF system consists of a large number of individual analog circuit blocks. As the system size increases, the traditional algorithms for circuit-level simulation do not accommodate the system-level simulation requirements. Additionally, time-domain transient analysis is effective for analog/digital co-simulation. However, for an analog/RF system, the wide-band input/output signals (e.g. the power spectral density for random noise) are best described by frequency-domain representations, as analyzing an analog/RF system in the time-domain over wide frequency bands can quickly become infeasible.